Binder composition for rechargeable lithium battery, preparing method of same, and rechargeable lithium battery including binder composition

ABSTRACT

A binder composition for a rechargeable lithium battery includes a semi-interpenetrating polymer network (semi-IPN) including a copolymer including a repeating unit represented by the following Chemical Formula 1 and a repeating unit represented by the following Chemical Formula 2 and polyacrylamide, and polyalkylene glycol. 
     
       
         
         
             
             
         
       
     
     In Chemical Formula 1, R 1  and R 2  are the same or different and are independently selected from hydrogen, or a substituted or unsubstituted C1 to C10 alkyl group, and R 3  and R 4  are an alkali metal. In Chemical Formula 2, R 5  to R 8  are the same or different, and are independently hydrogen, a substituted or unsubstituted C1 to C30 alkyl group, a substituted or unsubstituted C6 to C30 aryl group, or a substituted or unsubstituted C1 to C30 alkoxy group.

CROSS-REFERENCE TO RELATED APPLICATION

Korean Patent Application No. 10-2013-0079844, filed on Jul. 8, 2013, inthe Korean Intellectual Property Office, and entitled: “BinderComposition For Rechargeable Lithium Battery, Preparing Method Of Same,and Rechargeable Lithium Battery Including Binder Composition,” isincorporated by reference herein in its entirety.

BACKGROUND

1. Field

Embodiments are directed to a binder composition for a rechargeablelithium battery, a method of preparing the same, and a rechargeablelithium battery including the same.

2. Description of the Related Art

A rechargeable lithium battery includes positive and negative electrodesincluding a material that can reversibly intercalate/deintercalatelithium ions as positive and negative active materials and an organicelectrolyte solution or a polymer electrolyte solution charged betweenthe positive and negative electrodes. The positive and negativeelectrodes intercalate and deintercalate lithium ions and produceelectrical energy through oxidation and reduction reactions.

As for a positive active material for a lithium rechargeable battery, alithium-transition metal oxide being capable of intercalating lithiumsuch as LiCoO₂, LiMn₂O₄, LiNi_(1-x)Co_(x)O₂ (0<x<1), and the like hasbeen used.

As for a negative active material for a lithium rechargeable battery,various carbon-based materials such as artificial graphite, naturalgraphite, and hard carbon capable of intercalating and deintercalatinglithium ions have been used.

SUMMARY

Embodiments are directed to a binder composition for a rechargeablelithium battery, the binder composition including asemi-interpenetrating polymer network (semi-IPN) including:

a copolymer having a repeating unit represented by the followingChemical Formula 1 and a repeating unit represented by the followingChemical Formula 2 and polyacrylamide, and

polyalkylene glycol:

wherein,

R¹ and R² are the same or different and are independently selected fromhydrogen, or a substituted or unsubstituted C1 to C10 alkyl group, and

R³ and R⁴ are an alkali metal, and

wherein,

R⁵ to R⁸ are the same or different, and are independently hydrogen, asubstituted or unsubstituted C1 to C30 alkyl group, a substituted orunsubstituted C6 to C30 aryl group, or a substituted or unsubstituted C1to C30 alkoxy group.

The repeating unit represented by the above Chemical Formula 1 may beincluded in an amount of about 40 mol % to about 90 mol % based on thetotal amount of the copolymer. The repeating unit represented by theabove Chemical Formula 2 may be included in an amount of about 10 mol %to about 60 mol % based on the total amount of the copolymer.

In the semi-interpenetrating polymer network, a mole ratio of thecopolymer to the polyacrylamide may range from about 1:9 to about 5:5.

The binder composition may include about 50 mol % to about 95 mol % ofthe semi-interpenetrating polymer network and about 5 mol % to about 50mol % of polyalkylene glycol.

A weight-average molecular weight of the polyalkylene glycol may rangefrom about 400 g/mol to about 10,000 g/mol.

The binder composition may further include a free lithium ion (Li⁺).

The free lithium ion may be included in an amount of about 1 mol % toabout 10 mol % based on the sum of the copolymer and the polyacrylamide.

The binder composition may have a pH of about 8 to about 11.

A viscosity of the binder composition may range from about 1,000 cps toabout 100,000 cps.

Embodiments are also directed to a rechargeable lithium batteryincluding an electrode including the binder composition, as describedabove, and an electrode active material, and an electrolyte.

The electrode active material may include a silicon-based compound,graphite, or a combination thereof.

The electrode active material may include about 10 wt % to about 90 wt %of graphite.

A loading level of the electrode may range from about 4.5 g/cm² to about10 g/cm².

Embodiments are also directed to a method of preparing a bindercomposition for a rechargeable lithium battery, the method includingadding a copolymer of at least one monomer selected from an olefin-basedmonomer, an aromatic vinyl monomer, and an alkyl vinyl ether monomer anda cyclic unsaturated acid anhydride monomer, and polyalkylene glycol toa solvent, adding an alkali metal-containing compound to the resultantsolution, and adding an acrylamide monomer to the resultant solution toform polyacrylamide by polymerization and form a semi-interpenetratingnetwork structure of the copolymer and polyacrylamide.

The cyclic unsaturated acid anhydride monomer may be included in anamount of 40 mol % to 90 mol % based on the total amount of thecopolymer. The at least one monomer selected from the olefin-basedmonomer, aromatic vinyl monomer, and alkyl vinyl ether monomer may beincluded in an amount of about 10 to about 60 mol % based on the totalamount of the copolymer.

The polyalkylene glycol may be added in an amount of about 5 mol % toabout 50 mol % based on the sum of the copolymer, the polyacrylamide,and polyalkylene glycol.

During adding the alkali metal-containing compound to the solution, thealkali metal-containing compound may be included in an amount of about28 parts by weight to about 34 parts by weight based on 100 parts byweight of the copolymer.

A mole ratio of the copolymer to the polyacrylamide may range from about1:9 to about 5:5.

The method may further include, during performing polymerization andforming the semi-interpenetrating network structure after adding theacrylamide monomer to the solution, adding a polymerization initiator tothe solution.

The method may further include, after forming the semi-interpenetratingnetwork structure, adding a lithium-containing compound.

During adding the lithium-containing compound, the lithium-containingcompound may be added such that a content of a lithium ion is about 1mol % to about 10 mol % based on the sum of the copolymer and thepolyacrylamide.

BRIEF DESCRIPTION OF THE DRAWINGS

Features will become apparent to those of skill in the art by describingin detail exemplary embodiments with reference to the attached drawingsin which:

FIG. 1 illustrates a schematic view showing a structure of arechargeable lithium battery according to an embodiment.

FIG. 2 illustrates an infrared spectroscopy graph (IR) showing thebinder, and the like of Preparation Example 1.

FIG. 3 illustrates a thermogravimetric analysis graph showing thebinder, and the like of Preparation Example 1.

DETAILED DESCRIPTION

Example embodiments will now be described more fully hereinafter withreference to the accompanying drawings; however, they may be embodied indifferent forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey exemplary implementations to those skilled in the art. In thedrawing figures, the dimensions of layers and regions may be exaggeratedfor clarity of illustration.

As used herein, when a definition is not otherwise provided, the term“substituted” may refer to substitution with a C1 to C30 alkyl group; aC2 to C30 alkenyl group, a C2 to C30 alkynyl group, a C1 to C10alkylsilyl group; a C3 to C30 cycloalkyl group; C6 to C30 aryl group; aC1 to C30 heteroaryl group; or a C1 to C10 alkoxy group, instead of atleast one hydrogen of a compound.

As used herein, when a definition is not otherwise provided, the term“hetero” may refer to one selected from N, O, S, and P.

As used herein, when a definition is not otherwise provided, the term“alkyl group” may refer to “a saturated alkyl group” without any alkenylgroup or alkynyl group; or “an unsaturated alkyl group” including atleast one alkenyl group or alkynyl group. The term “alkenyl group” mayrefer to a substituent having at least one carbon-carbon double bond ofat least two carbons, and the term “alkyne group” may refer to asubstituent having at least one carbon-carbon triple bond of at leasttwo carbons. The alkyl group may be a branched, linear, or cyclic alkylgroup.

The alkyl group may be a C1 to C20 alkyl group, for example, a C1 to C6lower alkyl group, a C7 to C10 medium-sized alkyl group, or a C11 to C20higher alkyl group.

For example, a C1 to C4 alkyl group may have 1 to 4 carbon atoms in analkyl chain and may be selected from methyl, ethyl, propyl, iso-propyl,n-butyl, iso-butyl, sec-butyl, and t-butyl.

Examples of the alkyl group may be a methyl group, an ethyl group, apropyl group, an isopropyl group, a butyl group, an isobutyl group, at-butyl group, a pentyl group, a hexyl group, an ethenyl group, apropenyl group, a butenyl group, a cyclopropyl group, a cyclobutylgroup, a cyclopentyl group, a cyclohexyl group, or the like.

The term “aryl group” may refer to a cyclic substituent including allelements having a p-orbital which form conjugation and may refer to amonocyclic or fused ring (i.e., a plurality of rings sharing adjacentpairs of carbon atoms).

The substituted or unsubstituted C6 to C30 aryl group may be, forexample, a substituted or unsubstituted phenyl group, a substituted orunsubstituted naphthyl group, a substituted or unsubstituted anthracenylgroup, a substituted or unsubstituted phenanthryl group, a substitutedor unsubstituted naphthacenyl group, a substituted or unsubstitutedpyrenyl group, a substituted or unsubstituted biphenylyl group, asubstituted or unsubstituted p-terphenyl group, a substituted orunsubstituted m-terphenyl group, a substituted or unsubstitutedchrysenyl group, a substituted or unsubstituted triphenylenyl group, asubstituted or unsubstituted perylenyl group, a substituted orunsubstituted indenyl group, or a combination thereof, as examples.

As used herein, when a definition is not otherwise provided, the term“copolymerization” may refer to block copolymerization, randomcopolymerization, graft copolymerization, or alternatingcopolymerization, and the term “copolymer” may refer to a blockcopolymer, a random copolymer, a graft copolymer, or an alternatingcopolymer.

In an embodiment, a binder composition for a rechargeable lithiumbattery includes a semi-interpenetrating polymer network (semi-IPN)including a copolymer including a repeating unit represented by thefollowing Chemical Formula 1 and a repeating unit represented by thefollowing Chemical Formula 2 and polyacrylamide, and polyalkyleneglycol.

In the above Chemical Formula 1, R¹ and R² are the same or different andare independently selected from hydrogen, or a substituted orunsubstituted C1 to C10 alkyl group, and R³ and R⁴ are an alkali metal.

In the above Chemical Formula 2, R⁵ to R⁸ are the same or different, andare independently hydrogen, a substituted or unsubstituted C1 to C30alkyl group, a substituted or unsubstituted C6 to C30 aryl group, or asubstituted or unsubstituted C1 to C30 alkoxy group.

The semi-interpenetrating polymer network may have strong and toughcharacteristics and simultaneously may have excellent flexibility. Thebinder composition including the same may control expansion of an activematerial effectively, and may have improved adherence and stability withan electrolyte solution. In addition, the binder composition may be usedwith an aqueous solvent and thus may be environment-friendly. Arechargeable lithium battery including the binder composition mayprovide high capacity and excellent initial efficiency, charge anddischarge characteristics, and cycle-life characteristics.

The repeating unit represented by the above Chemical Formula 1 may bederived from a cyclic unsaturated acid anhydride monomer such as maleicanhydride, or the like. The copolymer may be dissolved in an aqueoussolvent due to the repeating unit represented by the above ChemicalFormula 1.

In the above Chemical Formula 1, R³ and R⁴ may be an alkali metal, and,for example, may be lithium, sodium, potassium, rubidium, cesium, or thelike. For example, R³ and R⁴ may be lithium. In this way, by using thecopolymer having a structure where an alkali metal is the substituent atthe R³ and R⁴ positions in the above Chemical Formula 1, the initialefficiency of a rechargeable lithium battery including the same may beimproved.

The repeating unit represented by the above Chemical Formula 1 may beincluded in an amount of about 40 mol % to about 90 mol % based on thetotal amount of the copolymer. For example, the repeating unit may beincluded in an amount of about 50 mol % to about 90 mol %, or about 50mol % to about 80 mol %. The copolymer and the binder compositionincluding the same may be dissolved in an aqueous solvent desirably, andflexibility and adherence may be ensured.

The repeating unit represented by the above Chemical Formula 2 may bederived from an olefin-based monomer, an aromatic vinyl monomer, analkyl vinyl ether monomer, or the like.

The olefin-based monomer may be, for example ethylene, propylene,butylene, isobutylene, 1-heptene, 1-decene, 1-octadecene, or the like,and the aromatic vinyl monomer may be styrene, o-ethyl styrene, m-ethylstyrene, p-ethyl styrene, α-methyl styrene, or the like. The alkyl vinylether monomer may be methylvinylether, ethylvinylether,propylvinylether, butylvinylether, or the like. These may be usedsingularly or as a mixture thereof.

The repeating unit represented by the above Chemical Formula 2 may beincluded in an amount of about 10 mol % to about 60 mol % based on thetotal amount of the copolymer. For example, the repeating unit may beincluded in an amount of about 10 mol % to about 50 mol %, or about 20mol % to about 50 mol %. Within the above range, the copolymer and thebinder composition including the same may have excellent flexibility,may be may be dissolved in an aqueous solvent, and may control expansionof an active material.

The copolymer forms a semi-interpenetrating network structure withpolyacrylamide. The binder composition includes a semi-interpenetratingpolymer network (semi-IPN), and the semi-interpenetrating polymernetwork includes the above-described copolymer and polyacrylamide.

The term “interpenetrating polymer network” (IPN) refers to a network ofheterogeneous polymers combined without a covalent bond. The term“semi-interpenetrating polymer network” (semi-IPN) refers to a networkstructure of a linear polymer and a cross-linking polymer.

Such a semi-interpenetrating polymer network may include two kinds ofpolymers in a chain shape to form a network structure, and may havestrength and toughness characteristics and excellent flexibilitycompared with a general copolymer. Accordingly, the binder compositionincluding the semi-interpenetrating polymer network may effectivelycontrol the expansion of an active material.

In the semi-interpenetrating polymer network, a mole ratio of thecopolymer to the polyacrylamide may range from about 1:9 to about 5:5.For example, the mole ratio may range from about 2:8 to about 5:5, orabout 2:8 to about 4:6.

The polyacrylamide may be included in an amount of about 50 mol % toabout 90 mol % based on the total amount of the semi-interpenetratingpolymer network. For example, the polyacrylamide may be included in anamount of about 50 mol % to about 80 mol %, or about 60 mol % to about80 mol %.

In this case, the semi-interpenetrating polymer network may ensureexcellent adherence and flexibility and thus, the binder composition mayeffectively control the expansion of an active material.

The polyalkylene glycol in the binder composition may help to reducecracks or bending of a binder layer when the binder composition iscoated and then dried, and may improve a loading level of an electrodeby improving a density of a wet film. Adherence with an active materialmay be maintained for a long time.

The polyalkylene glycol may include, for example, polymethylene glycol,polyethylene glycol, polypropylene glycol, polybutylene glycol,polyisobutylene glycol, and the like.

The weight-average molecular weight of the polyalkylene glycol may rangefrom about 400 g/mol to about 10,000 g/mol. For example, theweight-average molecular weight may range from about 400 g/mol to about9,000 g/mol, or about 400 g/mol to about 8,000 g/mol.

The binder composition may include about 50 mol % to about 95 mol % ofthe semi-interpenetrating polymer network. For example, thesemi-interpenetrating polymer network may be included in an amount ofabout 60 mol % to about 95 mol %, or about 70 mol % to about 95 mol %.

The binder composition may include about 5 mol % to about 50 mol %, or,for example, about 5 mol % to about 40 mol %, or about 5 mol % to about30 mol % of polyalkylene glycol. The binder composition may effectivelycontrol expansion of an active material and may improve cracks orbending problems of a binder layer during drying of the binder, and mayimprove a loading level of an electrode by improving a density of acoating layer for an active material layer before drying.

The binder composition may further include a free lithium ion (Li⁺). Arechargeable lithium battery including the binder composition may haveimproved charge and discharge characteristics.

The free lithium ion may be included in an amount of about 1 mol % toabout 10 mol % based on the sum of the copolymer and the polyacrylamide.For example, the free lithium ion may be included in an amount of about1 mol % to about 9 mol %, about 1 mol % to about 8 mol %, or about 1 mol% to about 7 mol %. Charge and discharge characteristics of a batterymay be effectively improved.

The binder composition may include a solvent in addition to thecopolymer and the free lithium ion. The solvent may be an organicsolvent or an aqueous solvent. The binder composition may be used withan aqueous solvent and may be environmentally friendly.

The binder composition may have a pH of about 8 to about 11. Forexample, the binder composition may have pH of about 8.5 to about 10.5.

The viscosity of the binder composition may range from about 1,000 cpsto about 100,000 cps. For example, the viscosity may range from about1,000 cps to about 50,000 cps, about 1,000 cps to about 40,000 cps,about 1,000 cps to about 30,000 cps, about 1,000 cps to about 20,000cps, about 1,000 cps to about 10,000 cps, or about 1,000 cps to about9,000 cps.

In another embodiment, a method of preparing a binder composition for arechargeable lithium battery includes adding a copolymer of at least onemonomer selected from an olefin-based monomer, an aromatic vinylmonomer, and an alkyl vinyl ether monomer, and a cyclic unsaturated acidanhydride monomer, and polyalkylene glycol to a solvent; adding to analkali metal-containing compound to the resultant solution, and addingan acrylamide monomer to the resultant solution to performpolymerization and form a semi-interpenetrating network structure of thecopolymer and polyacrylamide.

The binder composition prepared by the above method may effectivelycontrol expansion of an active material, and may have improved adherenceand stability with an electrolyte solution. The binder composition mayuse an aqueous solvent and may be environmentally friendly. In addition,a rechargeable lithium battery including the binder composition may havehigh capacity and excellent initial efficiency, charge and dischargecharacteristics and cycle-life characteristics.

The cyclic unsaturated acid anhydride monomer may be represented by thefollowing Chemical Formula 3.

In the above Chemical Formula 3, R¹ and R² may be the same or differentand may be independently selected from hydrogen or a substituted orunsubstituted C1 to C10 alkyl group.

The cyclic unsaturated acid anhydride monomer may be, for example maleicanhydride.

The amount of the cyclic unsaturated acid anhydride monomer may rangefrom about 40 mol % to about 90 mol % based on the total amount of thecopolymer. For example, the amount may range from about 40 mol % toabout 80 mol %, or about 50 mol % to about 80 mol %. The copolymer andthe binder composition including the same may be desirably dissolved inan aqueous solvent and flexibility and adherence may be ensured.

The amount of the at least one monomer selected from the olefin-basedmonomer, aromatic vinyl monomer, and alkyl vinyl ether monomer may rangefrom about 10 mol % to about 60 mol % based on the total amount of thecopolymer. For example, the amount may range from about 20 mol % toabout 50 mol %, or about 20 mol % to about 40 mol %. Within the aboverange, the copolymer and the binder composition including the same mayhave excellent flexibility, may be may be dissolved in an aqueoussolvent, and may control expansion of an active material.

The olefin-based monomer, aromatic vinyl monomer, and alkyl vinyl ethermonomer are the same as described above.

The polyalkylene glycol may be added in an amount of about 5 mol % toabout 50 mol % based on the sum of the copolymer, the polyacrylamide,and polyalkylene glycol. For example, the polyalkylene glycol may beadded in an amount of about 5 mol % to about 40 mol %, or about 5 mol %to about 30 mol %. The binder composition may exhibit reduced cracks orbending during drying, and the binder composition may improve a loadinglevel of an electrode by improving a density of a wet film.

The polyalkylene glycol is the same as described above.

When adding the alkali metal-containing compound to the solution, thealkali metal-containing compound may be included in an amount of about28 parts by weight to about 34 parts by weight based on 100 parts byweight of the copolymer.

The alkali metal of the alkali metal-containing compound, may be, forexample, lithium, sodium, potassium, rubidium, cesium, or the like. Forexample, the alkali metal may be lithium. The alkali metal-containingcompound may be an alkali metal hydroxide, an alkali metal salt, or thelike.

By adding the alkali metal-containing compound to the copolymer, thecopolymer may include a dicarboxyl repeating unit substituted with analkali metal, as in Chemical Formula 1. Thereby, initial efficiency of arechargeable lithium battery may be improved.

In the interpenetrating network structure, the mole ratio of thecopolymer to the polyacrylamide may range from about 1:9 to about 5:5.For example, the mole ratio may range from about 2:8 to about 5:5 orabout 2:8 to about 4:6. The polyacrylamide may be included in an amountof about 50 mol % to about 90 mol % based on the total amount of thesemi-interpenetrating polymer network. For example, the polyacrylamidemay be included in an amount of about 50 mol % to about 80 mol %, orabout 60 mol % to about 80 mol %. In this case, thesemi-interpenetrating polymer network may ensure excellent adherence andflexibility, and thereby, the binder composition may effectively controlexpansion of an active material.

The semi-interpenetrating network structure may be formed by anysuitable method. In one implementation, a first polymer may be primarilysynthesized and swelled, then a monomer of a second polymer, across-linking agent, an initiator, and the like may be added, and thesecond polymer may be synthesized in the presence of the first polymer.In another implementation, a first polymer and a second polymer may besynthesized according to a different mechanism from each other, amonomer or prepolymer of the first polymer, a monomer or prepolymer ofthe second polymer, a cross-linking agent, initiator, and the like maybe mixed to perform cross-linking polymerization of the first polymerand the second polymer simultaneously and to form thesemi-interpenetrating network structure.

The manufacturing method according to one implementation may provide thesemi-interpenetrating network structure by adding an acrylamide monomerand polymerizing the same in the presence of the copolymer.

In the manufacturing method, a cross-linking agent, a polymerizationinitiator, or the like may be added with the acrylamide monomer.

The polymerization initiator may include ammonium persulfate, sodiumpersulfate, potassium persulfate, hydrogen peroxide,2,2-azobis-(2-amidinopropane)dihydrochloride,2,2-azobis-(N,N-dimethylene)isobutyramidine dihydrochloride,2-(carbamoylazo)isobutyronitrile,2,2-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride,4,4-azobis-(4-cyanovaleric acid), ascorbic acid, benzoyl peroxide,dibenzoyl peroxide, lauryl peroxide, ditertiarybutyl peroxide, or thelike.

The manufacturing method may further include adding a lithium-containingcompound after forming the semi-interpenetrating network structure. Thebinder composition may further include a free lithium ion (Li⁺). Arechargeable lithium battery including the binder composition may haveimproved charge and discharge characteristics.

The lithium-containing compound may be added such that a content of thelithium ion is about 1 mol % to about 10 mol % based on the sum of thecopolymer and the polyacrylamide. For example, the lithium-containingcompound may be added such that a content of the lithium ion is about 1mol % to about 9 mol %, about 1 mol % to about 8 mol %, or about 1 mol %to about 7 mol %. Charge and discharge characteristics of a battery maybe effectively improved.

In another embodiment, a rechargeable lithium battery including theabove-described binder composition is provided. For example, therechargeable lithium battery may include electrodes and an electrolytesolution. The electrode includes a current collector and an activematerial layer positioned on the current collector. The active materiallayer includes an active material and the above-described bindercomposition.

The electrode active material may include a silicon-based compound suchas Si, SiO_(x), a Si—C composite, a Si-Q alloy, and the like, graphite,or a combination thereof. In SiO_(x), x may be in the range of 0<x<2,and in the Si-Q alloy, Q may be an alkali metal, an alkaline-earthmetal, a Group 13 to 16 element, a transition element, a rare earthelement, or a combination thereof, but is not Si.

When the negative active material is the silicon-based compound, abattery of high-capacity may be realized. For example, the battery mayhave a capacity of about 500 mAh/g to about 700 mAh/g.

However, the silicon-based negative active material undergoes volumeexpansion as a cycle goes, and a cycle-life of a general battery may bedeteriorated. When the silicon-based active material is used with theabove-described binder composition, on the other hand, the bindercomposition may effectively control the volume expansion of thesilicon-based negative active material, and cycle-life characteristicsof a battery may be improved.

In addition, the negative active material may include a combination ofthe silicon-based compound and graphite. In this case, a high-capacityand high power battery may be realized.

The negative active material may include about 10 wt % to about 90 wt %of graphite. For example, the negative active material may include about10 wt % to about 80 wt %, about 20 wt % to about 80 wt %, or about 30 wt% to about 60 wt % of graphite. In this case, a high-capacity and highpower battery may be realized.

A loading level of the electrode may range from about 4.5 g/cm² to about10 g/cm². For example, the loading level may range from about 4.5 g/cm²to about 9 g/cm², or about 4.5 g/cm² to about 8 g/cm². The term “loadinglevel of the electrode” refers to an amount of an active material perunit area of an electrode. The above-described binder composition may beappropriate for an electrode having the loading level within the range.

The electrode may include a positive electrode and a negative electrode.The binder composition according to one embodiment may be used in eitherthe positive electrode or the negative electrode.

According to an implementation, the binder composition may be applied tothe negative electrode.

The rechargeable lithium battery is described referring to FIG. 1. FIG.1 illustrates a schematic view showing a structure of a rechargeablelithium battery according to an embodiment.

Referring to FIG. 1, the rechargeable lithium battery 100 according tothis embodiment is a cylindrical battery that includes a negativeelectrode 112, a positive electrode 114, a separator 113 interposedbetween the negative electrode 112 and positive electrode 114, and anelectrolyte (not shown) impregnating the negative electrode 112, thepositive electrode 114, and separator 113, a battery case 120, and asealing member 140 sealing the battery case 120. The rechargeablelithium battery 100 may be manufactured by sequentially stacking thenegative electrode 112, separator 113, and positive electrode 114, andspiral-winding them, and housing the wound resultant in the battery case120.

The negative electrode 112 may include a current collector and anegative active material layer formed on the current collector.

The current collector may include a copper foil, a nickel foil, astainless steel foil, a titanium foil, a nickel foam, a copper foam, apolymer substrate coated with a conductive metal, or a combinationthereof.

The negative active material layer includes a negative active material,the binder composition, and optionally a conductive material.

The negative active material may include a material that reversiblyintercalates/deintercalates lithium ions, a lithium metal, a lithiummetal alloy, a material being capable of doping and dedoping lithium, ora transition metal oxide.

The material that reversibly intercalates/deintercalates lithium ionsmay be a carbon material, and may be any generally-used carbon-basednegative active material in a rechargeable lithium ion battery. Examplesthereof may include crystalline carbon, amorphous carbon, or acombination thereof. Examples of the crystalline carbon may be agraphite such as a shapeless, sheet-shaped, flake, spherical shaped orfiber-shaped natural graphite or artificial graphite, and examples ofthe amorphous carbon may be soft carbon or hard carbon, a mesophasepitch carbonized product, fired cokes, or the like.

The lithium metal alloy may include an alloy of lithium and a metal ofNa, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al,or Sn.

The material being capable of doping and dedoping lithium may be Si,SiO_(x) (0<x<2), a Si—C composite, a Si-Q alloy (wherein Q is an alkalimetal, an alkaline-earth metal, Group 13 to 16 elements, a transitionmetal, a rare earth element, or a combination thereof, and is not Si),Sn, SnO₂, a Sn—C composite, Sn—R (wherein R is an alkali metal, analkaline-earth metal, a Group 13 to 16 element, a transition metal, arare earth element, or a combination thereof, and is not Sn), and thelike. Specific examples of the Q and R may be Mg, Ca, Sr, Ba, Ra, Sc, Y,Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Tc, Re, Fe, Pb, Ru, Os, Rh, Ir, Pd,Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se,Te, Po, or a combination thereof.

The transition metal oxide may be vanadium oxide, lithium vanadiumoxide, or the like.

The binder composition is the same as described above, and descriptionsthereof are not repeated.

The conductive material may improve the electrical conductivity of theelectrode. Any suitable electrically conductive material that does notcause a chemical change may be used as the conductive material. Examplesthereof include a carbon-based material such as natural graphite,artificial graphite, carbon black, acetylene black, ketjen black, acarbon fiber, or the like; a metal-based material such as a metal powderor a metal fiber or the like of copper, nickel, aluminum, silver, andthe like; a conductive polymer such as a polyphenylene derivative or thelike; or a mixture thereof.

The positive electrode 114 includes a current collector and a positiveactive material layer formed on the current collector.

The current collector may be Al, as an example.

The positive active material layer may include a positive activematerial, the binder composition, and, optionally, a conductivematerial.

The positive active material may include lithiated intercalationcompounds that reversibly intercalate and deintercalate lithium ions.For example, at least one lithium metal composite oxide of lithium and ametal of cobalt, manganese, nickel, or a combination thereof may beused. Specific examples thereof include a compound represented by one ofthe following chemical formulae. Li_(a)A_(1-b)R_(b)D₂ (0.90≦a≦1.8 and0≦b≦0.5); Li_(a)E_(1-b)R_(b)O_(2-c)D_(c) (0.90≦a≦1.8, 0≦b≦0.5 and0≦c≦0.05); Li_(a)E_(2-b)R_(b)O_(4-c)D_(c) (0.90≦a≦1.8, 0≦b≦0.5,0≦c≦0.05); Li_(a)Ni_(1-b-c)Co_(b)R_(c)D_(α) (0.90≦a≦1.8, 0≦b≦0.5,0≦c≦0.05 and 0<α≦2); Li_(a)Ni_(1-b-c)Co_(b)R_(c)O_(2-α)Z_(α)(0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05 and 0<α<2);Li_(a)Ni_(1-b-c)Co_(b)R_(c)O_(2-α)Z₂ (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05 and0<α<2); Li_(a)Ni_(1-b-c)Mn_(b)R_(c)D_(α) (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05and 0<α≦2); Li_(a)Ni_(1-b-c)Mn_(b)R_(c)O_(2-α)Z_(α) (0.90≦a≦1.8,0≦b≦0.5, 0≦c≦0.05 and 0<α<2); Li_(a)Ni_(1-b-c)Mn_(b)R_(c)O_(2-α)Z₂(0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05 and 0<α<2); Li_(a)Ni_(b)E_(c)G_(d)O₂(0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5 and 0.001≦d≦0.1);Li_(a)Ni_(b)Co_(c)Mn_(d)GeO₂ (0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0≦d≦0.5 and0.001≦e≦0.1); Li_(a)NiG_(b)O₂ (0.90≦a≦1.8 and 0.001≦b≦0.1);Li_(a)CoG_(b)O₂ (0.90≦a≦1.8 and 0.001≦b≦0.1); Li_(a)MnG_(b)O₂(0.90≦a≦1.8 and 0.001≦b≦0.1); Li_(a)Mn₂G_(b)O₄ (0.90≦a≦1.8 and0.001≦b≦0.1); QO₂; QS₂; LiQS₂; V₂O₅; LiV₂O₅; LiTO₂; LiNiVO₄;Li_((3-f))J₂(PO₄)₃ (0≦f≦2); Li_((3-f))Fe₂(PO₄)₃ (0≦f≦2); and LiFePO₄.

In the above chemical formulae, A is Ni, Co, Mn, or a combinationthereof; R is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element,or a combination thereof; D is O, F, S, P, or a combination thereof; Eis Co, Mn, or a combination thereof; Z is F, S, P, or a combinationthereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combinationthereof; Q is Ti, Mo, Mn, or a combination thereof; T is Cr, V, Fe, Sc,Y, or a combination thereof; and J is V, Cr, Mn, Co, Ni, Cu, or acombination thereof.

The positive active material may include the positive active materialwith a coating layer, or a compound of the active material and theactive material coated with the coating layer. The coating layer mayinclude a coating element compound of an oxide of a coating element, ahydroxide of a coating element, an oxyhydroxide of a coating element, anoxycarbonate of a coating element, or a hydroxycarbonate of a coatingelement. The compound for the coating layer may be either amorphous orcrystalline. The coating element included in the coating layer may beMg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixturethereof. The coating process may include any suitable process (e.g.,spray coating, dipping), as long as it does not causes any side effectswith respect to the properties of the positive active material.

The binder composition may be the above-described binder composition, ora generally-used binder.

Examples of the generally-used binder may include polyvinyl alcohol,carboxylmethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose,polyvinylchloride, carboxylated polyvinylchloride, polyvinylfluoride, anethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane,polytetrafluoroethylene, polyvinylidene fluoride, polyethylene,polypropylene, a styrene-butadiene rubber, an acrylatedstyrene-butadiene rubber, an epoxy resin, nylon, or the like.

The conductive material improves the electrical conductivity of theelectrode. Any suitable electrically conductive material that does notcause a chemical change may be used. Examples thereof include naturalgraphite, artificial graphite, carbon black, acetylene black, ketjenblack, carbon fiber, copper, nickel, aluminum, silver, or the like, ametal powder, a metal fiber, or the like, and one or more kinds of aconductive material such as a polyphenylene derivative or the like maybe mixed.

The negative electrode 112 and the positive electrode 114 may bemanufactured by mixing each active material, a conductive material, anda binder in a solvent to prepare an active material composition, andcoating the composition on a current collector. The solvent may beN-methylpyrrolidone or water but is not limited thereto.

The electrolyte may include a non-aqueous organic solvent and a lithiumsalt.

The non-aqueous organic solvent may serve as a medium for transmittingions taking part in the electrochemical reaction of a battery.

The non-aqueous organic solvent may include a carbonate-based,ester-based, ether-based, ketone-based, alcohol-based, or aproticsolvent. The carbonate-based solvent may include dimethyl carbonate(DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropylcarbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate(MEC), ethylene carbonate (EC), propylene carbonate (PC), butylenecarbonate (BC), or the like. The ester-based solvent may include methylacetate, ethyl acetate, n-propyl acetate, dimethylacetate,methylpropionate, ethylpropionate, γ-butyrolactone, decanolide,valerolactone, mevalonolactone, caprolactone, or the like. Theether-based solvent may include dibutyl ether, tetraglyme, diglyme,dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran or the like.The ketone-based solvent may include cyclohexanone, or the like. Thealcohol-based solvent may include ethanol, isopropyl alcohol, or thelike. The aprotic solvent may include nitriles such as R—CN (wherein Ris a C2 to C20 linear, branched, or cyclic hydrocarbon group, and mayinclude a double bond, an aromatic ring, or an ether bond), amides suchas dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolanes, orthe like.

The non-aqueous organic solvent may be used singularly or in a mixture.When the organic solvent is used in a mixture, its mixture ratio can becontrolled in accordance with desirable performance of a battery.

The carbonate-based solvent may be prepared by mixing a cyclic carbonateand a linear carbonate. The cyclic carbonate and the linear carbonatemay be mixed together in a volume ratio of about 1:1 to about 1:9, whichmay enhance the performance of an electrolyte.

The non-aqueous organic solvent may include an aromatichydrocarbon-based organic solvent as well as the carbonate basedsolvent. The carbonate-based solvent and the aromatic hydrocarbon-basedorganic solvent may be mixed together in a volume ratio of about 1:1 toabout 30:1.

The aromatic hydrocarbon-based organic solvent may be an aromatichydrocarbon-based compound represented by the following Chemical Formula4.

In the above Chemical Formula 4, R¹⁰ to R¹⁵ may be the same or differentand may be selected from hydrogen, a halogen, a C1 to C10 alkyl group, ahaloalkyl group, and a combination thereof.

Specific examples of the aromatic hydrocarbon-based organic solvent maybe selected from benzene, fluorobenzene, 1,2-difluorobenzene,1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene,1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene,1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene,1,2,4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene,1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene,1,2,4-triiodobenzene, toluene, fluorotoluene, 2,3-difluorotoluene,2,4-difluorotoluene, 2,5-difluorotoluene, 2,3,4-trifluorotoluene,2,3,5-trifluorotoluene, chlorotoluene, 2,3-dichlorotoluene,2,4-dichlorotoluene, 2,5-dichlorotoluene, 2,3,4-trichlorotoluene,2,3,5-trichlorotoluene, iodotoluene, 2,3-diiodotoluene,2,4-diiodotoluene, 2,5-diiodotoluene, 2,3,4-triiodotoluene,2,3,5-triiodotoluene, xylene, and a combination thereof.

The non-aqueous electrolyte may further include vinylene carbonate or anethylene carbonate-based compound represented by the following ChemicalFormula 5 in order to improve cycle-life of a battery.

In the above Chemical Formula 2, R¹⁶ and R¹⁷ are the same or differentand are selected from hydrogen, a halogen, a cyano group (CN), a nitrogroup (NO₂), and a fluorinated C1 to C5 alkyl group, provided that atleast one of R₇ and R₈ is selected from a halogen, a cyano group (CN), anitro group (NO₂), and a fluorinated C1 to C5 alkyl group, and R¹⁶ andR¹⁷ are not simultaneously hydrogen.

Examples of the ethylene carbonate-based compound include difluoroethylenecarbonate, chloroethylene carbonate, dichloroethylene carbonate,bromoethylene carbonate, dibromoethylene carbonate, nitroethylenecarbonate, cyanoethylene carbonate, fluoroethylene carbonate, or thelike. The use amounts of additives for improving the cycle life may beadjusted within an appropriate range.

The lithium salt is dissolved in the non-aqueous solvent, supplieslithium ions in a rechargeable lithium battery, basically operates therechargeable lithium battery, and improves lithium ion transfer betweenpositive and negative electrodes. The lithium salt may include at leastone supporting salt selected from LiPF₆, LiBF₄, LiSbF₆, LiAsF₆,LiC₄F₉SO₃, LiClO₄, LiAlO₂, LiAlCl₄,LiN(C_(x)F_(2x+1)SO₂)(C_(y)F_(2y+1)SO₂) (wherein, x and y are naturalnumbers), LiCl, LiI, LiB(C₂O₄)₂ (lithium bis(oxalato) borate, LiBOB), ora combination thereof. The lithium salt may be used in a concentrationof about 0.1M to about 2.0M. When the lithium salt is included at theabove concentration range, an electrolyte may have excellent performanceand lithium ion mobility due to optimal electrolyte conductivity andviscosity.

A separator may be present between the positive electrode and negativeelectrode depending on a kind of a rechargeable lithium battery. Such aseparator may include polyethylene, polypropylene, polyvinylidenefluoride, or a multilayer thereof, for example, a mixed multilayer suchas a polyethylene/polypropylene double-layered separator,polyethylene/polypropylene/polyethylene triple-layered separator,polypropylene/polyethylene/polypropylene triple-layered separator, andthe like.

The following Examples and Comparative Examples are provided in order tohighlight characteristics of one or more embodiments, but it is to beunderstood that the Examples and Comparative Examples are not to beconstrued as limiting the scope of the embodiments, nor are theComparative Examples to be construed as being outside the scope of theembodiments. Further, it is to be understood that the embodiments arenot limited to the particular details described in the Examples andComparative Examples.

Synthesis Example 1 Synthesis of Binder Composition

390 g of deionized water, 25 g of isobutylene-co-maleic anhydride, and10 g of polyethylene glycol were put in a 2 L reactor having a heater, acooler, and an agitator, an aqueous solution prepared by dissolving 8.0g of lithium hydroxide in 80 g of deionized water at room temperaturewas slowly added thereto, and the mixture was agitated for 10 minutes.The reactor was heated up to 80° C. under nitrogen atmosphere andmaintained for 3 hours. Subsequently, a solution prepared by dissolving0.125 g of ammonium persulfate in 10 g of deionized water was added tothe resultant, the mixture was maintained for 20 minutes, and an aqueoussolution prepared by dissolving 65 g of acrylamide in 180 g of deionizedwater was added thereto in a dropwise fashion for 2 hours. The mixturewas reacted for 1 hour and cooled down to less than or equal to 40° C.,an aqueous solution prepared by dissolving lithium 2.9 g of hydroxide in20 g of deionized water was added thereto in a dropwise fashion for 10minutes, the mixture was packed, obtaining a binder having a solidcontent of 15.0 wt %, pH 9.8, and viscosity of 5,000 cps. The binderincluded a semi-interpenetrating polymer network including a copolymerincluding a repeating unit represented by the following Chemical Formula1 and a repeating unit represented by the following Chemical Formula 2and polyacrylamide, and polyalkylene glycol, and included free lithiumion.

In the above Chemical Formula 1, R¹ and R² are hydrogen, and R³ and R⁴are Li.

In the above Chemical Formula 2, R⁵ and R⁷ are hydrogen, and R⁶ and R⁸are CH₃.

The repeating unit represented by the above Chemical Formula 1 wasincluded in an amount of 40 mol % based on the total amount of thecopolymer, and the repeating unit represented by the above ChemicalFormula 2 was included in an amount of 60 mol % based on the totalamount of the copolymer. Furthermore, in the semi-interpenetratingpolymer network, a mole ratio of the copolymer to the polyacrylamide was3:7. The amount of the semi-interpenetrating polymer was 90 mol % andthat of polyalkylene glycol was 10 mole % in the binder composition.

The weight-average molecular weight of the polyalkylene glycol was 3000g/mol, and the amount of free lithium ion was 6.6 mol %.

Evaluation Example 1 Spectroscopy Analysis (IR) of Binder

FIG. 2 illustrates a spectroscopy analysis (IR) graph of four kinds ofcompounds: a poly isobutylene-co-maleic anhydride lithium salt (LPIBMA),polyacrylamide (PAM), a mixture of LPIBA and PAM, and a binder having asemi-interpenetrating polymer network (LPIMAM37(B)) according toPreparation Example 1.

Referring to a top graph 1 in FIG. 2, an IR peak of the binder(LPIMAM37(B)) according to Preparation Example 1, an amide III peakshifted from 1314 cm⁻¹ to 1349 cm⁻¹ and 1322 cm⁻¹. This may be caused bya molecular interaction between a functional group of the LPIBMA and anamide group of the PAM. The peak shift may be interpreted as showingthat the isobutylene-co-maleic anhydride lithium salt and thepolyacrylamide form a semi-interpenetrating network structure.

In addition, a peak at 1100 cm⁻¹ due to C—O stretching of polyethyleneglycol was found.

Evaluation Example 2 Thermogravimetric Analysis (TGA)

Thermogravimetric analysis of a mixture of LPIBA and PAM and a binder(LPIMAM37(B)) synthesized according to Preparation Example 1 wasperformed, and the results are provided in FIG. 3. As shown in FIG. 3,the binder according to Preparation Example 1 showed improved thermalresistance compared with the simple mixture of two polymers.

Examples and Comparative Examples Manufacture of Rechargeable LithiumBattery Cell

A negative active material slurry was prepared by mixing each componentin the amounts in water provided in the following Table 1. The negativeactive material slurry was coated onto a copper foil, dried at 110° C.to evaporate water, and compressed, manufacturing a negative electrode.The negative electrode was made into a 16 mm disk. Each negativeelectrode according to the Examples and Comparative Examples was loadedaccording to the load levels provided in the following Table 2.

A positive electrode was manufactured including mixing an activematerial (LiNi_(0.6)CO_(0.2)Mn_(0.2)O₂), a conductive material (Denkablack), and a binder (polyvinylidene fluoride) in a weight ratio of94:3:3 in N-methylpyrrolidone to prepare slurry. The positive electrodewas formed into a 14 mm disk.

Using a polypropylene separator and an electrolyte solution prepared bymixing ethylene carbonate (EC), diethyl carbonate (DEC), and fluoroethylene carbonate (FEC) in a volume ratio of 5:70:25 and adding LiPF₆in a concentration of 1.5 mol/L in the mixed solvent, and theseelectrodes, a rechargeable lithium battery cell was fabricated.

TABLE 1 Examples Comparative Examples 1 2 1 2 3 4 Active Silicon-based45.5 45.5 45.5 45.5 45.5 45.5 material Alloy (v6 from 3M) Graphite 45.545.5 45.5 45.5 45.5 45.5 Conductive Ketjen black 2 1 1 1 1 1 materialBinder Synthesis 8 8 Example 1 LPIBMA 8 SBR 4 1.5 CMC 4 1.5 PAI 8

Each component in Table 1 was used as a unit of wt %.

Each component provided in Table 1 is illustrated as follows.

Active Material

A silicon-based active material, V6 made by 3M was used as the alloy,and MC20 made by Mitsubishi Chemical Co. was used as graphite.

Conductive Material

KB600JD ketjen black made by Mitsubishi Chemical Co. was used.

Binder

LPIBMA is a poly isobutylene-co-maleic anhydride lithium salt, and SBRis a styrene butadiene rubber. CMC indicates carboxylmethyl cellulose,and PAI indicates polyamideimide.

Evaluation Example 1 Evaluation of Initial Efficiency

The rechargeable lithium battery cells according to Examples andComparative Examples were charged and discharged at 0.1 C, then, chargecapacity and discharge capacity of the rechargeable lithium batterycells were measured, a ratio of the discharge capacity relative to thecharge capacity was calculated, and the results are provided in thefollowing Table 2.

Evaluation Example 2 Evaluation of Cycle-Life Characteristics

A capacity ratio of capacity at 100 cycles relative to capacity at 1cycle of the rechargeable lithium battery cells according to Examplesand Comparative Examples was calculated, and the results are provided inthe following Table 2.

TABLE 2 Examples Comparative Examples 1 2 1 2 3 4 Initial efficiency (%)86 89 80 76 — — Cycle-life characteristics (%) 90 92 58 68 — — Loadinglevel (g/cm²) 5 5 5 5 5 5

As shown in Table 2, the rechargeable lithium battery cells according toExamples showed remarkably improved initial efficiency and cycle-lifecharacteristics compared with the rechargeable lithium battery cellsaccording to Comparative Examples.

By way of summation and review, recently, demand for a battery havinghigh energy density increasingly has made a negative active materialhaving high theoretical capacity density desirable. Accordingly, Si, Sn,and Ge alloyed with lithium, an oxide thereof, an alloy thereof havedrawn attention.

In particular, a Si-based negative active material has very high chargecapacity and is widely applied to a high-capacity battery. However, aSi-based negative active material may expand by about 300% to about 400%during charging and discharging. Thus, charge and dischargecharacteristics and cycle-life characteristics of a battery may bereduced.

Accordingly, research on a binder capable of effectively controllingexpansion of the Si-based negative active material has been activelyconducted. Particularly, research for a binder composition capable ofeffectively controlling expansion of the active material has beenactively performed.

Embodiments provide a binder composition for a rechargeable lithiumbattery capable of effectively controlling expansion of an activematerial, having improved adherence and stability with an electrolytesolution, capable of increasing a loading level of an electrode, andreducing cracks or bending during drying.

Another embodiment provides a method of manufacturing the same.

Still another embodiment provides a rechargeable lithium battery havingimproved initial efficiency, charge and discharge characteristics, andcycle-life characteristics due to the binder composition.

Example embodiments have been disclosed herein, and although specificterms are employed, they are used and are to be interpreted in a genericand descriptive sense only and not for purpose of limitation. In someinstances, as would be apparent to one of ordinary skill in the art asof the filing of the present application, features, characteristics,and/or elements described in connection with a particular embodiment maybe used singly or in combination with features, characteristics, and/orelements described in connection with other embodiments unless otherwisespecifically indicated. Accordingly, it will be understood by those ofskill in the art that various changes in form and details may be madewithout departing from the spirit and scope thereof as set forth in thefollowing claims.

What is claimed is:
 1. A binder composition for a rechargeable lithiumbattery, the binder composition comprising: a semi-interpenetratingpolymer network (semi-IPN) including: a copolymer having a repeatingunit represented by the following Chemical Formula 1 and a repeatingunit represented by the following Chemical Formula 2, andpolyacrylamide, and polyalkylene glycol

wherein, R¹ and R² are the same or different and are independentlyselected from hydrogen, or a substituted or unsubstituted C1 to C10alkyl group, and R³ and R⁴ are an alkali metal, and

wherein, R⁵ to R⁸ are the same or different, and are independentlyhydrogen, a substituted or unsubstituted C1 to C30 alkyl group, asubstituted or unsubstituted C6 to C30 aryl group, or a substituted orunsubstituted C1 to C30 alkoxy group.
 2. The binder composition for arechargeable lithium battery as claimed in claim 1, wherein: therepeating unit represented by Chemical Formula 1 is included in anamount of about 40 mol % to about 90 mol % based on a total amount ofthe copolymer, and the repeating unit represented by Chemical Formula 2is included in an amount of about 10 mol % to about 60 mol % based onthe total amount of the copolymer.
 3. The binder composition for arechargeable lithium battery as claimed in claim 1, wherein in thesemi-interpenetrating polymer network, a mole ratio of the copolymer tothe polyacrylamide ranges from about 1:9 to about 5:5.
 4. The bindercomposition for a rechargeable lithium battery as claimed in claim 1,wherein the binder composition includes: about 5 mol % to about 50 mol %of polyalkylene glycol, based on a sum of the copolymer, thepolyacrylamide, and the polyalkylene glycol.
 5. The binder compositionfor a rechargeable lithium battery as claimed in claim 1, wherein aweight-average molecular weight of the polyalkylene glycol ranges fromabout 400 g/mol to about 10,000 g/mol.
 6. The binder composition for arechargeable lithium battery as claimed in claim 1, wherein the bindercomposition further comprises a free lithium ion (Li⁺).
 7. The bindercomposition for a rechargeable lithium battery as claimed in claim 6,wherein the free lithium ion is included in an amount of about 1 mol %to about 10 mol % based on a sum of the copolymer and thepolyacrylamide.
 8. The binder composition for a rechargeable lithiumbattery as claimed in claim 1, wherein the binder composition has a pHof about 8 to about
 11. 9. The binder composition for a rechargeablelithium battery as claimed in claim 1, wherein a viscosity of the bindercomposition ranges from about 10,000 cps to about 100,000 cps.
 10. Arechargeable lithium battery, comprising: an electrode including thebinder composition as claimed in claim 1, and an electrode activematerial; and an electrolyte.
 11. The rechargeable lithium battery asclaimed in claim 10, wherein the electrode active material includes asilicon-based compound, graphite, or a combination thereof.
 12. Therechargeable lithium battery as claimed in claim 10, wherein theelectrode active material includes about 10 wt % to about 90 wt % ofgraphite.
 13. The rechargeable lithium battery as claimed in claim 10,wherein a loading level of the electrode ranges from about 4.5 g/cm² toabout 10 g/cm².
 14. A method of preparing a binder composition for arechargeable lithium battery, the method comprising: adding a copolymerof at least one monomer selected from an olefin-based monomer, anaromatic vinyl monomer, and an alkyl vinyl ether monomer and a cyclicunsaturated acid anhydride monomer, and polyalkylene glycol to asolvent; adding an alkali metal-containing compound to the resultantsolution; and adding an acrylamide monomer to the resultant solution toform polyacrylamide by polymerization and form a semi-interpenetratingnetwork structure of the copolymer and polyacrylamide, wherein: the atleast one monomer selected from an olefin-based monomer, an aromaticvinyl monomer, and an alkyl vinyl ether monomer and the cyclicunsaturated acid anhydride monomer are selected such that the copolymerhas a repeating unit represented by the following Chemical Formula 1 anda repeating unit represented by the following Chemical Formula 2,

wherein, R¹ and R² are the same or different and are independentlyselected from hydrogen, or a substituted or unsubstituted C1 to C10alkyl group, and R³ and R⁴ are an alkali metal, and

wherein, R⁵ to R⁸ are the same or different, and are independentlyhydrogen, a substituted or unsubstituted C1 to C30 alkyl group, asubstituted or unsubstituted C6 to C30 aryl group, or a substituted orunsubstituted C1 to C30 alkoxy group.
 15. The method as claimed in claim14, wherein: the cyclic unsaturated acid anhydride monomer is includedin an amount of 40 mol % to 90 mol % based on a total amount of thecopolymer, and the at least one monomer selected from the olefin-basedmonomer, aromatic vinyl monomer, and alkyl vinyl ether monomer isincluded in an amount of about 10 to about 60 mol % based on the totalamount of the copolymer.
 16. The method as claimed in claim 14, whereinthe polyalkylene glycol is added in an amount of about 5 mol % to about50 mol % based on a sum of the copolymer, the polyacrylamide, andpolyalkylene glycol.
 17. The method as claimed in claim 14, wherein,during adding the alkali metal-containing compound to the solution, thealkali metal-containing compound is included in an amount of about 28parts by weight to about 34 parts by weight based on 100 parts by weightof the copolymer.
 18. The method as claimed in claim 14, wherein a moleratio of the copolymer to the polyacrylamide ranges from about 1:9 toabout 5:5.
 19. The method as claimed in claim 14, wherein the methodfurther comprises, during performing polymerization and forming thesemi-interpenetrating network structure after adding the acrylamidemonomer to the solution, adding a polymerization initiator to thesolution.
 20. The method as claimed in claim 14, wherein the methodfurther comprises, after forming the semi-interpenetrating networkstructure, adding a lithium-containing compound.
 21. The method asclaimed in claim 20, wherein, during adding the lithium-containingcompound, the lithium-containing compound is added such that a contentof a lithium ion is about 1 mol % to about 10 mol % based on a sum ofthe copolymer and the polyacrylamide.